Drained system.
Closed Ball Valves (BV) & Gate Valves (GV) to hold pressure from compressor.
Removed bonnet & poppet assembly from Febco 765 Back Flow Preventer (BFP).
Installed expansion plug in top of BFP.
Attached compressor line to Febco 765 VB.
Opened ball valve on test port & closed off ball valve in top port of BFP.
Closed ball valve & spigot below BFP.
Ran all (12) zone to confirm water in lines.
Charged system to 50 psi.
Opened zone #1 via Toro Controller.
Released compressed air 50 PSI to zone #1 (longest line first).
Water blown out of zone #1 sprinklers – not aggressive stream or mist like previous years.
Attempted to repeat for zone #2 – sprinklers didn’t rise & no water from sprinklers.
Noticed zone #11 sprinklers was leaking water – bubbling only, and also zone #9 was spouting some water.
Cleaned diaphragms on both zone valves & that corrected the leakage problem.
Tried to blow out remaining zones, but only zones #8 & 11 spewed any water, not aggressively.
Remaining sprinklers did not rise, but could feel very slight amount of air from sprinklers.
Where did the residual water go from last lawn watering?
Was there a crack in the main line to funny pipes due to freezing over past winter, therefore self draining, yet I watered lawn all summer?
No water leakage in zone valve box.
Confirmed air was reaching zone valves & sprinklers, although very low pressure at most sprinkler heads.

Second attempt to blow water out of irrigation lines (Have to confirm there was no water left on lines, otherwise would freeze if not blown out):

So I started over by watering the lawn again for each of the 12 zones for a couple minute each just to be sure there was water in lines to start with when blowing out the system (again). I repeated all of the above with same results: could not blow water out of the zones.
Again, I confirmed pressurized air was reaching the zone valves for each of zones #7-#12. Also, with the controller off, jar cap on tightly, and solenoid removed, air really flowed through the solenoid port. After putting the solenoid back on, there still wasn’t water coming out of the sprinklers for that zone.
When I applied 50 PSI air pressure & checked the sprinklers there is the tiniest indication of air/bubbles coming out, but no water. Is the water still in the lines?
Sounds like the air in the lines are not pushing the water through, like there is a major leak somewhere that is common to all main lines. Yet the system will push the water through when watering normally.

If the pressurized air can get to the zone valves, why can’t it get to the sprinklers? Is there a common major leak that affects all the zones?

I replaced the 9V alkaline battery in the controller with a 9V rechargeable battery as instructed in the manual (warning given about possible damage if use alkaline battery). I thought the battery only affected the display, yet could this affect the solenoids or other components in the system? Getting desperate I guess - freezing temps ahead.

Your air source might be sub-par. This is your homeowner compressor? What's the hose?

Just as an aside, you are best off replacing the Flo-Pro valves, with something like the Irritrol 2500TF. That flow control on each zone valve can be a lifesaver when zones might get stuck open during winterizing.

Thanks for your comment. The air pressure is 60 PSI (3/8" ID hose) and is maintained at that level pretty well. The compressor is 33 gal with a max of 150 PSI, regulated to 60 PSI.

I decided to open up the water to the irrigation system, let the pressure build up to 60 PSI on the water tank & then turned on the controller, but did not turn on any of the zones. I wanted to see what would happen if the zone valves just saw water pressure in the manifold.

I then walked every zone/every sprinkler & noted whether or not they were leaking, even just dribbling water. If they did, then that would indicate a leaking zone valve which would rob water pressure from a zone valve that was actually turned on. The same would apply with air pressure. It turned out that there were 6 that were leaking, 4 from zones in the rear lawn & 2 from the front lawn. In fact, one of the front lawn sprinklers was not only leaking it was spraying water at full throttle, as though I had turned it on.

So,I then disassembled the 5 zone valves for the rear lawn & washed/rinsed the internals (diaphragm/bonnet/spring/tube) & the valve seat thoroughly. These are Toro zone valves. The ones in front are Hunter zone valve.

I ran out of time & was too pooped to pop to do all 6 valves. I'll finish when weather permits.

In any event, if the zone valves out back continue to leak I’ll have to replace all the Toro valves. I’ve done what I can. Besides, these are twenty years old, so perhaps it’s time. If so I'll go with Hunter PGV valves as they are readily available locally, although the Irritrol 2500TF does look good.

This post has been edited 3 times, last edit by "AlL" (Oct 9th 2017, 8:40am)